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Automotive Suppliers Roll Out 42-V Power-Bus Parts

David G. Morrison | Dec 03, 2000

At the recent Convergence2000 conference and exhibition, automotive suppliers presented further evidence that 42-V electrical systems are just over the horizon. Industry executives forecast that vehicles with a 42-V power bus may be just a few years away, as automakers strive to meet the growing demand for electrical power. Judging by the various 42-V power components introduced at the show, the industry is indeed gearing up for the coming shift in vehicular power architecture.

The first step will be the introduction of cars with dual 42- and 12-V electrical systems. These mixed-voltage systems will be needed to deal with lamps and other 12-V legacy loads that may be phased out eventually. Steve Gladstein of Robert Bosch Corp., which is working to develop dual 42-/12-V systems, estimates that dual-voltage systems may be on the market as early as 2004. Remnants of the 12-V system, though, may remain in production as late as 2015.

But the company predicts that 42-V-only systems will replace the dual-voltage systems in most high-end vehicles, by as soon as 2008. Bosch is developing two such components. One is a 42-V Lundell alternator able to deliver 3.5 kW. The other is an integrated starter-alternator (ISA) designed to supply 10 kW of mechanical power with approximately 2 kW of electrical power at idle.

Meanwhile, Siemens Automotive expects its integrated starter-generator (ISG, another name for ISA) to be powering sport utility vehicles by 2005 (see the figure). With fuel-saving features such as start-stop operation and recapture of braking energy, the ISG should boost SUV fuel efficiency by up to 25%. The ISG's peak output is 8 kW with better than 80% efficiency across the entire speed range. A conventional alternator may supply 1.5 kW at a maximum efficiency of 70% (only 30% at high speeds).

Of course, a generator is just one element of a vehicular power system, which must include components for power distribution, management, and energy storage. Naturally, these functions become more complex as the system evolves from 12-V only to dual 42-/12-V systems. To address some of this complexity, Yazaki North America Inc. and Johnson Controls Inc. developed a scalable nodal active power (SNAP) architecture to provide active power and load management.

SNAP contains two main elements: the SNAP Source Module, and the SNAP Gateway. The module holds all of the power-generation components, including Johnson's 42-V AGM batteries and Smart Charge Management Control. It also contains a dual-voltage power-distribution box. The Gateway provides a pulse-width-modulated (PWM) 42-V supply equal to 14 V rms to power existing lighting systems. The gateway allows scalable local distribution of 42 V dc or PWM 42 V to reduce the complexity of the power-distribution system.

Several 42-V products were introduced at the component level. On Semiconductor announced an enhanced current-mode PWM controller (CS51022A) that steps 42 V down to 14 V at 6 A. On's series of 80-V power MOSFETs (NTMD3N08L and others) are sampling. In circuit protection, Fujitsu Takamisawa America Inc. debuted a 42-V relay (FBR580).